Auto merge of #38960 - arielb1:blake-endian, r=michaelwoerister

Use little-endian encoding for Blake2 hashing on all architectures

Like many hash functions, the blake2 hash is mathematically defined on
a sequence of 64-bit words. As Rust's hash interface operates on
sequences of octets, some encoding must be used to bridge that
difference.

The Blake2 RFC (RFC 7693) specifies that:
```
   Byte (octet) streams are interpreted as words in little-endian order,
   with the least-significant byte first.
```

So use that encoding consistently.

Fixes #38891.

Beta-nominating since this is a regression since 1.15.

r? @michaelwoerister